Technical Abstract:
Rice and red rice growing together in the rice fields create favorable conditions for outcrossing because of their morphological similarities and oftentimes synchronous flowering. In 2000, experiments were designed to determine the reciprocal outcrossing rates by planting pairs of rice and red rice with near synchronous flowering. In 2002, at least 2300 seeds produced from two of the pairs were planted in a greenhouse. DNA was extracted from leaves of the 14-day-old seedlings and fingerprinted using microsatellite (SSR) markers; RM 215, RM 234, RM 251, and RM 253. Outcrossing between Kaybonnet rice and AR1994-8 awned, black-hulled red rice was estimated at 0.10% with AR1994-8 as the pollen donor, but was not detectable with Kaybonnet as the pollen donor. Outcrossing between Starbonnet rice and AR1994-11D awned, straw-hulled red rice was estimated at 0.23% with AR1994-11D as the pollen donor and 0.14% with Starbonnet as the pollen donor. Although preliminary and speculative, these data suggest that weed-crop architecture may have affected the reciprocal gene flow. Taller plants (usually red rice) appear more likely to function as pollen donors than acceptors, while shorter plants (usually rice) appear more likely to function as pollen acceptors than donors. The degree to which flowering periods of rice and red rice overlap will influence heavily the potential for outcrossing and gene flow. The sizable biological variability in the red rice populations that infest rice fields will probably complicate the dynamics of outcrossing and gene flow between rice and red rice.